The present invention relates to a rotation balancing mechanism for balancing orbiting scrolls of scroll-type compressors.
FIGS. 9 and 10 show a prior art scroll-type compressor. The scroll type compressor includes a motor housing 15 for a motor 12 and a compressor housing 31 for a compression mechanism 13. A support frame 16 is attached to the front of the motor housing 15. The compressor housing 31 is fixed to the support frame 16. The motor 12 includes a drive shaft 18. The compression mechanism 13 includes a fixed scroll 32 and an orbiting scroll 33, which includes a base plate 36. A crankshaft 51 is located between the drive shaft 18 and the orbiting scroll 33 to cause the orbiting scroll 33 to orbit. Bearing sleeves 63 are formed on the support frame 16. Bearing sleeves 66 are formed on the rear and peripheral surface of the base plate 36 of the orbiting scroll 33. Follower crankshafts 61 arc located between the bearing sleeves 63 and the outer bearing sleeves 66. The follower crankshafts 61 permit orbital movement of the orbiting scroll 33 and prevent rotation about its own axis of the orbiting scroll 33.
The orbiting scroll 33 orbits with the crank shaft 51 while rotation about its own axis of the orbiting scroll 33 is prevented by the follower crankshafts 61. This movement draws refrigerant gas from a suction chamber 39, compresses the gas in a compression chamber 38, and discharges the gas to an external refrigerant circuit through a discharge port 41. The compression chamber 38 is defined by the fixed scroll 32 and the orbiting scroll 33.
The center of gravity of the orbiting scroll 33 is located at an axis O2 of an eccentric pin 53. When the orbiting scroll 33 orbits during the operation of the compressor, a centrifugal force is applied to the eccentric pin 53. The centrifugal force is based on the moment of inertia about the axis O1 of the crankshaft 51 (drive shaft 18). That is, centrifugal force FT (WT*R1*.omega..sup.2) is applied to the eccentric pin 53. R1 represents the distance between the axis O1 of the drive shaft 18 and the axis O2 of the eccentric pin 53, which is the orbiting radius of the orbiting scroll 33. The mass of the orbiting scroll 33 that orbits the axis O2 is represented by WT. The orbiting speed (angular velocity) of the orbiting scroll 33 is represented by .omega.. Therefore, a central balance weight 57, which has a mass W, is integrally attached to the crankshaft 51. The balance weight is located on the opposite side of crankshaft 51 from the eccentric pin 53 with respect to the axis O1. The central balance weight 57 achieves dynamic balancing, that is, the net centrifugal force applied to the crankshaft 51 is null.
In the prior art scroll-type compressor shown in FIGS. 9 and 10, since the central balance weight 57 is attached only to the crankshaft 51, the following problem occurs. As shown in FIG. 10, to offset the centrifugal force FT of the orbiting scroll 33 with the single central balance weight 57, the center of gravity G1 of the central balance weight 57 must be radially spaced from the axis O1 of the drive shaft 18 and the central balance weight 57 cannot be compact. Therefore, the central path C1, which is the path of the periphery of the central balance weight 57, is relatively large.
On the other hand, the peripheral surfaces of the outer bearing sleeves 66, which support the eccentric pins 65 of the follower crankshafts 61, must not interfere with the central path C1. As a result, journal shafts 62 of the follower crankshafts 61 and outer bearing sleeves 66 are obliged to be located to extend radially from peripheral rim of the base plate 36 of the orbiting scroll 33 as shown in FIG. 10. Accordingly, to avoid interference between the outer paths C2, which are the paths of the peripheral surfaces of the outer bearing sleeves 66, and the inner surface of the housing 31, projections 31a must be formed on the housing 31. This increases radial size of the compressor housing 31.
Japanese Unexamined Utility Model Publication No. 1-61480 shows a compressor that is similar to the compressor of FIGS. 9 and 10. As shown in FIG. 11, the follower crankshafts 61 of the compressor shown in the publication include balance weights 81, which compensate for the mass imbalance of the crankshafts 61 when orbiting. In this case, since each balance weight 81 is formed perpendicular to a corresponding eccentric pin 65, trim weights 82, which nullify the centrifugal force of the corresponding follower crankshaft 61, are attached to the follower crankshafts 61. Therefore, the journal shafts 62 are rearwardly extended by the trim weights 82.
In the above scroll-type compressor of FIG. 11, only the balance weight that is attached to the drive crankshaft opposes the centrifugal force caused by the mass of the orbiting scroll. Therefore, the follower crankshafts 61 and the outer bearing sleeves 66 extend radially outward from the base plate 36 of the orbiting scroll 33, which increases the size of the compressor housing 31. In addition, the trim weights 82 complicate the structure and increase the mass of the compressor.